Recently, there have been developed, methods of refining aluminum in a blast furnace. In the conventional methods, such as disclosed in U.S. Pat. No. 3,661,561, oxygen preheated to approximately 1,000.degree. C. is blown into a blast furnace through a plurality of tuyeres of the furnace. In these processes, in order for the refining of aluminum in the blast furnace to be successful, it has been important subject how efficiently the preheated oxygen was generated and supplied to the furnace. One of the prior heater devices used in an experiment produced the hot oxygen by effecting the heat exchange between oxygen of room temperature and a fluid generated by another heat source. However, in the experiment using this particular heater device, the amount of the produced hot oxygen was several tens of thousand Nm.sup.3 /h. Consequently, it is not economical to apply the above-mentioned way of preheating oxygen to the preheating process when there is no utilizable heat source and when a specific heat source must be newly prepared.
Also, the use of hot oxygen in the refining process of steel or zinc, has been suggested. It is desired in this case to provide a device that can produce and supply a great amount of hot oxygen safely and efficiently.
In the refining of iron or aluminum, air or oxygen-enriched air is supplied to a furnace through the tuyere or the lance of the furnace after it is heated up to a high temperature. An example of the heater which is applicable to this refining is shown in Japanese Published Unexamined Patent Application No. 59-501278. This heater, i.e., a burner which also serves as a lance is used for heating metal products in a fusion furnace. Oxygen is discharged in a jet from the nozzle of the burner and fuel is supplied from the conduit concentrically surrounding the nozzle. The supplied fuel is then jetted into the discharged oxygen and is burned with the oxygen, which produces hot oxygen including combustion gas. Depending on the purpose, the oxygen content of the combustion gas is controlled and the heater is used either as a burner or as a lance for hot oxygen containing combustion gas.
However, there arises a problem of the temperature of the peripheral portion of the burner rising severely since the construction of the burner is such that fuel supplied from the nozzle-surrounding conduit is jetted into and mixed with the oxygen flow and is burned within the burner so that the hot combustion gas including oxygen is produced.
These days, there are used, burners which utilize pulverized coal as their main fuel for the purpose of melting steel scrap, aluminum, copper and the like. These burners must produce flames having stable temperatures of not less than approximately 2,000.degree. C. so that the burners have the required melting capacity. However, the combustion rate of pulverized coal is extremely slow in comparison with that of a liquid fuel such as fuel oil or a gaseous fuel such as CH.sub.4, C.sub.3 H.sub.8 and the like. Also, the flame temperature of pulverized coal is lower than that of the liquid or gaseous fuel. It is not easy to produce a stable flame by the monofuel combustion of pulverized coal. The flame due to the monofuel combustion is unstable and sometimes extinguished when the temperature of the atmosphere in the vicinity of the burner in a furnace is low, causing its radiant heat to be reduced. For these reasons, there have been used, burners which utilize a gaseous or liquid fuel such as LPG, natural gas, fuel oil and the like, and the pulverized coal has been used as the fuel of combination burners which also use a liquid or gaseous fuel along with the pulverized coal. However, the combination burners are not economical enough since the mixture ratio of liquid or gaseous fuel must be increased, that is, the consumption of the pulverized coal must be decreased in order for the combination burners to produce flames of high temperature.
FIG. 1 shows an instance of the conventional combination burner which uses pulverized coal mixed with a liquid fuel. This burner has six cylinders coaxially disposed to each other, wherein the innermost cylinder is a conduit 231 for supplying liquid fuel, the cylinder surrounding the conduit 231 is a conduit 232 for supplying auxiliary combustion gas for assisting the combustion of the liquid fuel, the cylinder surrounding the conduit 232 is a conduit 233 for supplying pulverized coal, the cylinder surrounding the conduit 233 is a conduit 234 for supplying auxiliary combustion gas for assisting the combustion of the pulverized coal, and the last cylinder surrounding the conduit 234 is a jacket 235 for circulating cooling water. The liquid fuel-supplying conduit 231 is provided at its front end with a nozzle 236 for discharging the liquid fuel supplied through the conduit 231 in a jet. Also, the auxiliary combustion gas-supplying conduit 232 is provided at its front end with a ring 237 which forms the nozzle for discharging the auxiliary combustion gas in a jet. The auxiliary combustion gas is jetted from the annular opening 238 defined by both the outer periphery of the nozzle 236 and the ring 237, and is mixed with the liquid fuel to produce a primary flame. Reference numeral 239 denotes a cylinder which defines a main combustion chamber 240 in cooperation with the liquid fuel nozzle 236, the front end of the auxiliary combustion gas-supplying conduit 232 and the front end of the pulverized coal-supplying conduit 233. The rear end of the main combustion chamber 240 is in fluid communication with an outlet 241 of the pulverized coal-supplying conduit 233. Around the outlet 241, an outlet 242 for jetting a part of auxiliary combustion gas is open and is in communication with the rear end of the main combustion chamber 240. The pulverized coal discharged from the outlet 241 is mixed with the auxiliary combustion gas discharged from the outlet 242 and is burned by the assistance of the primary flame by the liquid fuel, producing a secondary flame. In front of the combustion chamber 240, a sub-combustion chamber 243 is defined by the inner face of the auxiliary combustion gas-supplying conduit 234 and the front face of main combustion chamber 240. The remainder of the auxiliary combustion gas is jetted into the sub-combustion chamber 243 through the space between the cylinder 239 and the conduit 234, and surrounds the primary and secondary flames to achieve a perfect combustion. In short, in the conventional burners, the flame produced by the liquid fuel and the flame produced by the pulverized coal are combined and form a unitary flame.
As has been described, although it has been planned and tested the blowing of hot oxygen into smelting furnaces upon refining ferrous and nonferrous metals, there has been no oxygen heater, so far, which can efficiently heat an extremely large quantity of oxygen without severely lowering the purity of the oxygen and which is concerned about the safety and durability of itself during the heating process.
Also, the conventional burner uses an unnecessarily large amount of fuel since the hot combustion gas in the vicinity of the burner is cooled by the cooling water circulating in the jacket of the burner, increasing the heat loss. As a result, there arises a problem of the oxygen content of the combustion gas being decreased. That is, the decrease of the oxygen content is not desirable upon the refining of ferrous and nonferrous metals such as, in particular, the fused reduction of aluminum.
Furthermore, there has existed no monofuel combustion burner, for use in a furnace such as an electric furnace for steel scrap, fusion furnace for aluminum and a reverberatory furnace for copper, which is capable of producing a stable flame of high temperature and has a excellent fusing ability even if it is used at regions in the furnaces where the temperature of the atmosphere in the vicinity of burner is relatively low.
The present invention is proposed regarding the above-mentioned situation. An object of the present invention is to provide an oxygen heater which is capable of heating a large quantity of oxygen efficiently without severely lowering the purity of oxygen and which is concerned about the safety and durability of itself during the heating process.
Another object of the present invention is to provide an oxygen lance having an oxygen heater which has a compact construction and reduces the heat loss such as, in particular, the heat loss in the combustion gas-producing region, thereby producing hot gas having a high oxygen content.
A further object of the present invention is to provide a pulverized solid fuel burner in which the pulverized solid fuel is used as the main fuel and gaseous or liquid fuel is used merely for preheating auxiliary combustion gas.